Pseudomonas fluorescens is a common Gram-negative, rod-shaped bacterium^[1]. It belongs to the Pseudomonas genus; 16S rRNA analysis has placed P. fluorescens in the P. fluorescens group within the genus^[2], to which it lends its name.

General characteristics

P. fluorescens has multiple flagella. It has an extremely versatile metabolism, and can be found in the soil and in water. It is an obligate aerobe but certain strains are capable of using nitrate instead of oxygen as a final electron acceptor during cellular respiration.

Optimal temperatures for growth of Pseudomonas fluorescens are 25-30 degrees Celsius. It tests positive for the oxidase test.

Heat stable lipases and proteases are produced by Pseudomonas fluorescens and other similar pseudomonads ^[3]. These enzymes cause milk to spoil, by causing bitterness, casein breakdown, and ropiness due to production of slime and coagulation of proteins ^[4][5].

The name

The word Pseudomonas means 'false unit', being derived from the Greek words pseudo (Greek: ????? 'false') and monas (Latin: monas, fr. Greek: ?????/?????? 'a single unit'). The word was used early in the history of microbiology to refer to germs. The name 'fluorescens' is because secretes a soluble fluorescent pigment called pyoverdin (formerly called fluorescein), which is a type of siderophore^[6].

Genome sequencing projects

The genomes of P. fluorescens strains SBW25^[7], Pf-5^[8] and PfO-1^[9] have been sequenced.

Biocontrol properties

Some P. fluorescens strains (CHA0 or Pf-5 for example) present biocontrol properties, protecting the roots of some plant species against parasitic fungi such as Fusarium or Pythium, as well as some phytophagous nematodes^[10].

It is not clear exactly how the plant growth promoting properties of P. fluorescens are achieved; theories include:

• that the bacteria might induce systemic resistance in the host plant, so it can better resist attack by a true pathogen
• the bacteria might out compete other (pathogenic) soil microbes, e.g. by siderophores giving a competitive advantage at scavenging for iron
• the bacteria might produce compounds antagonistic to other soil microbes, such as phenazine-type antibiotics or hydrogen cyanide

There is experimental evidence to support all of these theories, in certain conditions; a good review of the topic is written by Haas and Defago^[11].

Medical Properties

By culturing Pseudomonas fluorescens, Mupirocin (an antibiotic) can be produced, which has been found to be useful in treating skin, ear and eye disorders^[12]. Mupirocin free acid and its salts and esters are agents currently used in creams, ointments, and sprays as a treatment of Methicillin-resistant Staphylococcus aureus (MRSA) infection.

P. fluorescens demonstrates hemolytic activity and as a result has been known to infect blood transfusions^[13].

It is also used in milk to make yogurt.

United States Patents: 6489358, 4873012, 6156792

Disease

P. fluorescens is an unusual cause of disease in humans, and usually affects patients with compromised immune systems (e.g., patients on cancer treatment). From 2004 to 2006, there was an outbreak of P. fluorescens in the United States, involving 80 patients in six states. The source of the infection was contaminated heparinized saline flushes using in cancer patients.^[14]

References

External links

• www.pseudomonas.com, the Pseudomonas genome database
• Migula's Systematic Bacteriology (in German)
• UV fluorescent Pseudomonas video

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